FIG. 1 depicts a schematic diagram of a portion of a typical wireless telecommunications system in the prior art, which system provides wireless telecommunications service to a number of wireless terminals (e.g., wireless terminals 101-1 through 101-3) that are situated within a geographic region. The heart of a typical wireless telecommunications system is Wireless Switching Center ("WSC") 120, which may also be known as a Mobile Switching Center ("MSC") or Mobile Telephone Switching Office ("MTSO"). Typically, Wireless Switching Center 120 is connected to a plurality of base stations (e.g., base stations 103-1 through 103-5) that are dispersed throughout the geographic area serviced by the system and to local- and toll-offices (e.g., local-office 130, local-office 138 and toll-office 140). Wireless Switching Center 120 is responsible for, among other things, establishing and maintaining calls between wireless terminals and between a wireless terminal and a wireline terminal, which is connected to the system via the local and/or long-distance networks.
The geographic area serviced by a wireless telecommunications system is partitioned into a number of spatially distinct areas called "cells." As depicted in FIG. 1, each cell is schematically represented by a hexagon; in practice, however, each cell usually has an irregular shape that depends on the topology of the terrain serviced by the system. Typically, each cell contains a base station, which comprises the radios and antennas that the base station uses to communicate with the wireless terminals in that cell and also comprises the transmission equipment that the base station uses to communicate with Wireless Switching Center 120.
For example, when wireless terminal 101-1 desires to communicate with wireless terminal 101-2, wireless terminal 101-1 transmits the desired information to base station 103-1, which relays the information to Wireless Switching Center 120. Upon receipt of the information, and with the knowledge that it is intended for wireless terminal 101-2, Wireless Switching Center 120 then returns the information back to base station 103-1, which relays the information, via radio, to wireless terminal 101-2.
Typically, a cell can contain dozens or hundreds of wireless terminals, each of which is either powered-on or powered-off. When a wireless terminal powers on and desires to either register with Wireless Telecommunications System 120 or to place a call, the wireless terminal transmits a hail to the base station serving the cell containing the wireless terminal.
FIG. 2 depicts a schematic diagram of wireless terminal 101-1 as it transmits a hail to base station 103-1. Base station 103-1 comprises N radios that can receive the hail and the probability that any one radio will receive the hail is substantially close to 1/N, in well-known fashion. If the radio is functioning properly, the radio will respond to the hail and initiate the process of registration.
In contrast, if the radio is not functioning at all, then the radio will fail to respond to the hail and the process of registration will not commence. In accordance with the prior art, a hail from a particular wireless terminal will always be received by a particular radio. Therefore, the problem exists that if the radio is not functioning and fails to respond to the hail, subsequent hails by the wireless terminal will also be received by the faulty radio and the wireless terminal will be effectively precluded from receiving service.
Furthermore, because wireless telecommunications system 100 does not know when or where a wireless terminal will transmit a hail, it is likely that a hail can be directed towards a radio in wireless telecommunications system 100 without wireless telecommunications system 100 knowing it. In other words, wireless telecommunications system 100 cannot distinguish between a functioning radio that simply receives no hails and a malfunctioning radio to which one or more hails are directed but not acknowledged because the radio is broken.
To add to the complexity of the problem, many malfunctioning radios suffer intermittent or graduated faults, in contrast to catastrophic faults. Therefore, a malfunctioning radio suffering an intermittent or graduated fault might, for example, receive 10 hails but only acknowledge and initiate registration for 8 of them. For the purposes of this specification, a radio that is totally broken is said to be suffering a "hard" fault. In contrast, a radio that is partially functioning because it has intermittent or graduated faults is said to be suffering a "soft" fault.
The presence of a faulty radio in wireless telecommunications system 100 is problematic for several reasons. First, when the user of a wireless terminal attempts access to wireless telecommunications system 100 and is unable to get service, the user usually gets frustrated or annoyed and that is bad for business for the operator of wireless telecommunications system 100. In addition, the operator of wireless telecommunications system 100 only gets paid when the system actually gets used, and if a radio is broken, then the operator loses money. Therefore, the need exists for a technique for quickly and reliably determining when a radio is suffering a fault.
Self-diagnostic test circuitry could be incorporated into the radio, but test circuitry has the disadvantage of increasing the complexity and cost of the radio itself. Furthermore, sometimes the test circuitry itself malfunctions and a properly functioning radio is declared by the test circuitry to be malfunctioning. In that case, a craftsperson is sent to inspect and repair the radio. In general, it is prohibitively expensive and annoying to assign craftspeople to fix radios that are not, in fact, broken.
As an alternative, a craftsperson could periodically inspect and test each radio using special-purpose test equipment, but skilled craftspeople are expensive and the process of inspection is invasive, which itself introduces the potential for damaging the radio.
Therefore, the need exists for a technique for determining when a radio is suffering a hard or soft fault in a manner that is less expensive and more reliable than techniques in the prior art.